Examine source code of Start Page

{
  "manifest_version": 2,
  "version": "1.2.3",
  "name": "Start Page",
  "description": "A start page with many useful features.",
  "chrome_url_overrides": {
    "newtab": "index.html"
  },
  "chrome_settings_overrides": {
    "homepage": "index.html"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "startpage@notmario.net"
    }
  },
  "icons": {
    "48": "icon.svg",
    "96": "icon.svg"
  }
}